Attapulgite clay filter aid product and method of making same



3,080,214.- Patented Mar'. 5, 1963 3,080,214 ATTAPULGITE CLAY FILTER AIDPRODUCT AND METHOD OF MAKING SAW James B. Duke, Metuchen, and Ernest W.Greene, Westfield, NJ, assignors to Minerals 8: Chemicals PhilipplCoiglporation, Menlo Park, N..l'., a corporation of Maryan No Drawing.Continuation of applications Ser. No.

848,498 and Ser. No. 848,553, Oct. 26, 1959. This application Jan. 25,M61, Ser. No. 84,774 11 Claims. (Cl. 23-410) The present invention,which is a continuation of copending applications Serial No. 848,498,filed October 26, 1959 and now abandoned and Serial No. 848,553, filedOctober 26, 1959, and now abandoned, relates to a novel magnesiumaluminosilicate product, useful particularly as a filter aid, and to themethod of producing the same from attapulgite clay.

Filtration is a widely used operation in the chemical industries and isbasically a straining operation designed to remove suspended solids froma liquid. Thus, filtration should be distinguished from decolorizationoperations in which liquids are treated with solid adsorbents whichremove soluble color body impurities by a mechanism involvingadsorption. A filter aid, which is a. finely divided solid, may beprecoated on the filter support and is usually also mixed with theliquid to be filtered. Filtration removes both the filter aid andforeign solids from the liquid, and the filter aid added with the liquidgradually forms a rigid, permeable incompressible cake on the filtercloth or screen. Fine solids originally suspended in the liquid aresimultaneously entrained in the cake as it is built up and the porousnature of the cake prevents such solids from agglomerating and formingan impervious layer on the filter cloth or screen. Filtration of liquidthrough the porous bulky cake is thus more rapid and efficient than itwould be in the absence of a filter aid. By proper choice of filter aid,a consistently high degree of clarification may be realized while stilloperating at an efiicient filter rate with small dosage of filter aid.Filter rate or flow rate is defined as the volume of impure liquidpassed through a unit area of filter cake per unit of time and isusually expressed as gallons per square foot per hour. There is a fairlygeneral inverse correlation between flow rate and clarification capacityof filter aid products. Flow rate and clarity factors vary with the typeof liquid being filtered, filter pressure, quantity and nature of filteraid used, etc.

In addition to satisfactory flow rate and clarification capacity, otherproperties are necessary for a good filter aid. These include inertness,cake stability, and cake adhesiveness.

Diatomaceous silica filter aids have dominated industrial filtration formany years. The high flow rates and brilliant clarity achieved throughthe use of such filter aids is believed to be due to the uniquevariegated structure of the silica diatoms which interlace themselves inthe filter cake to form numerous traps for even submicroscopic particleswhile still providing interstices between particles to insure good cakepermeability. Diatomaceous filter aids are supplied in regular milled,calcined, and flux-calcined grades, the various grades diifering infilter rates and clarification capacity in various filtration processes.In general, the preparation of all grades may be considered a dryprocess involving removing of impurities, controlled drying, calcination(when employed), and particle size classification. Commerciallyavailable filter aid grades of diatomaceous earth are essentially pureamorphous silica in the form of a plurality of geometrical shapes, suchas filiforrn, spicular, denticular, and plankton disc.

Many attempts have been made to produce filter aid powders competitivewith the diatomaceous silica materials so as to provide new markets forother materials as Well as to supply competitive or superior products.To date no material has been found which has supplanted diatomaceousfilter aids in their principal applications, e.g., in sugar refining andin clarifying dry cleaning solvents, beers and wines. The use of clays(particularly specially processed clays) as filter aids has beenattempeted in the past. None of the prior art procedures has provided aclay-derived product which has met industrial acceptance as hasdiatomaceous silica. In fact clay, which is frequently indigenous todiatomite, deposits, is considered to be such an undesirable contaminantin a diatornaceous filter aid that present day processes for treatingraw diatomaceous earth for filter aid use include operationsspecifically intended to remove clay.

Clays are hydrated aluminum silicates in which iron or magnesium mayproxy in whole or in part for the aluminum. Clay minerals may beclassified on the basis of their crystalline structure. Most clays havea micaceous sheet structure. For example, kaolin clays are composed of atwo-layer type mineral, and the montmorillonite clay minerals (e.g.,bentonites) are of the threelayer type. In contrast with theaforementioned micaceous-type clays are attapulgite and sepiolite whichare members of a unique class of clays characterized by a chainlikestructure, similar to the amphibole structure, and are composed ofchains of silica tetrahedrons linked together by octahedral groups ofoxygens and hydroxyls containing aluminum and magnesium atoms.Attapulgite, a hydrated magnesium aluminosilicate, is the principalmineral constituent of Georgia-Florida fullers earth which usuallycontains, in addition to attapulgite, varying minor amounts of quartz,sepiolite and/or montmorillonite minerals and iron minerals. A typicalchemical analysis of attapulgite clay is as follows:

Percent Total volatile matter 19.93 Free moisture 12.10 Volatile freebasis:

SiO- 68.43 A1 0 12.56 F3203 MgO 9.82 CaO 1.67 K 0 0.70 Na O 0.25 'liO0.60 Others I 1.03

In raw attapulgite clay, the ultimate colloidally dimensioned acicularparticles are oriented in a random brush-heap fashion. The ultimateattapulgite crystals composing the clay aggregate are so small they canbe discerned only through the use of an electron microscope. Thus, whenviewed under an optical microscope the aggregates of raw clay give noindication of the needlelike form of the plurality of attapulgitecrystals composing them. In contrast, individual silica diatoms havemicroscopic dimensions and the unique geometrical shape of diatoms isreadily perceived by examining a sample of idiatomaceous earth with anoptical microscope, using for example a magnification of 800. Therefore,it is apparent that silica diatoms and attapulgite crystals difi'erappreciably in their size. The shape factor which contributes to theutility of diatomaceous earth as a filter aid is not present inattapulgite clay aggregates in which the attapultige needles areconsiderably too small to function in the manner similar to that ofsilica diatoms.

Raw attapulgite clay is in fact completely unsatisfactory as a filteraid in that it tends to disperse in and thicken a liquid to be filtered.This is especially true of polar liquids such as water. Therefore,attapulgite clay in its naturally occurring condition functions in amanner which is the antithesis of a filter aid. It is known that thethickening or gel-forming property of attapulgite clay can be reduced oreliminated by calcining the clay. Calcination, among other things,removes water from the clay lattice and when properly controlled itenhances the adsorption properties of attapulgite clay. For this reasonthe controlled calcination is frequently referred to as activation.Industrial attapulgite clay adsorbent are usually activated bycalcination at temperatures within the range of about 600 F. to 1000" F.to reduce the volatile matter to about 1% to 6%. This reduction involatile matter represents a reduction of some, but not all, of thecombined water. It is known that when attapulgite clay is calcined attemperatures considerably higher than those mentioned above, such astemperatures of about 1100 F. or more with a reduction of the volatilematter below the 1% level, the value of the material as an adsorbent issharply decreased. The term volatile matter (V.M.) refers to the weightpercent of a material eliminated when the material is heatedsubstantially to constant Weight at about 1700 F. In the case of rawclay, volatile matter is essentially water. The term free moisture(Rh/L), as used herein, refers to the weight percent of a materialeliminated when the material is heated substantially to constant weightat 220 F.

While activation, especially in conjunction with controlled sizing,enhances the utility of the clay as an adsorbent for removing solubleimpurities from various liquids, such as soluble coloring matter inoils, activated adsorbent grades of attapulgite clay, even when groundto a suitable fine particle size, are not competitive with diatomaceousearth as filter aids. The principal reason is that, in spite of the factthat the activated clay afiords a good flow rate when used with clearliquids, the same is not true when attempts are made to use theactivated clay to clarify liquids containing suspended impurities. Forexample, the process of U.S. 2,390,490, Atwell, has to do with a methodfor processing activated attapulgite clay to improve the flow rate ofliquids therethrough. The improvement consists in controlling the dryingof the raw clay before it is milled and activated. In this mannerdetrimental fines in the activated product are limited. We have foundthat the Atwell process, while providing a material with anexceptionally good flow rate for clear liquid, does not result in theproduction of a material which has a good flow rate when used in afiltration operation on solutions containing fine solid impurities insuspension (as opposed to soluble adsorbable impurities). As a result,Atwells material is more useful as a decolorizing agent for adsorptionof foreign color body impurities from a liquid than it is inclarification operations in which suspended impurities are to be removedfrom a liquid. The product provided by the Atwell method has also beenfound to leave much to be desired as a filter aid in the clarificationof present day organic dry cleaning solutions which contain expensivedetergents. Georgia- Florida fullers earth processed in accordance withprior art activation processes tends to adsorb and deplete detergentsfrom the dry cleaning solutions and is unacceptable for this reason.

Accordingly, an object of the present invention is to provide a filteraid product from attapulgite clay which will overcome the aforementioneddifficulties.

An important object of the invention is the transforma tion ofattapulgite clay into a novel lo-w bulk density, anhydrous magnesiumaluminosilicate product having essentially the same volatile freechemical analysis as attapulgite clay but differing in physical form,properties and potential fields of use from forms of attapulgite clay orother materials presently known.

A more specific object of the invention is to provide a filter aidproduct from attapulgite clay, which product possesses clarification andflow rate properties in indusl trial filtration operations, such as insugar refining, as good as or superior to those of high qualitydiatomaceous earth filter aids presently used for the purpose.

Still another object of the invention is the provision of a filter aidpowder from attapulgite clay which may be used in the clarification ofdry cleaning solvents containing detergents with minimal adsorption ofthe detergent.

Still another object of the invention is a novel method of processingattapulgite clay.

Other objects and features of our invention will be apparent from thedescription thereof which follows.

The present invention is a result of our discovery that a novelamorphous anhydrous magnesium aluminosilicate product, resemblingcertain filiform diatoms in size, form and utility, can be prepared fromattapulgite clay, but not from the micaceous-type clays such as kaolinand bentonite clays, by a wet process hereafter described.

Broadly stated, the method of the present invention comprises theinitial step of agitating a small amount of colloidal attapulgite clayin water containing a defiocculating agent for the clay, thereby forminga defiocculated aqueous slip of the clay in which aggregates of the clayare dispersed substantially completely into ultimate col loidallydimensioned acicular attapulgite particles. The fluid deflocculated claydispersion thus produced is dried to a grindable consistency byevaporation of water therefrom while maintaining the fluid dispersionquiescentthat is, without appreciable boiling of the slip and withoutagitating the slip during drying.

The dried material is milled to a fine powder prior to a calcinationtreatment at extremely high temperature for a time sufiic-ient toeliminate substantially completely water of composition from theattapulgite crystals without fusing the material. The calcinattion iscarried out at tem peratures appreciably higher than temperatures usedin activating attapulgite clay for use as an industrial adsorbent. Thecalcined product, which is a pulverulent mass, is then pulverized toprovide the desired filter aid powder.

The resultant magnesium aluminosilicate product consists predominatelyof particles which may be distinctly discerned in an optical microscope(at 810 magnification, for example), as discrete or clustered elongatedparticles, similar to fibers or rods and generally unsymmetrical inform. The particles are similar in size to the filiform or aciculardiatomite particles at the same magnification although the latterusually exhibit a higher degree of symmetry and appear to have straightsurfaces, as opposed to the irregular surfaces of the particles of theproduct of our invention. Chemically, our magnesium al-uminosilicateproduct has essentially the same analysis as volatile free attapulgiteclay although it contains a very small amount of a deflocculating agentused in the initial state of its production. The V.M. of our product isless than 1% and usually is close to 0.

Our novel form of attapulgite bears no resemblance to its attapu'lgiteprecursor. Attapulgite in its raw, hydrous state is crystalline andproduces a characteristic X-ray diffraction pattern. The product of ourinvention is substantially anhydrous, by way of contrast with thehydrated attapulgite, and it is distinctly amorphous, as determined byX-ray diffraction procedure.

While both attapulgite crystals and our calcined particles may bedescribed as being elongated, these particles differ considerably fromeach other in the order of magnitude of dimensions of particles. Ourmagnesium aluminosilicate particles for the most part are about 2 toabout 4 microns wide, more usually 2 to 3 microns wide, with a lengthwithin the range of about 5 to about 50 microns, and more usually withinthe range of 10 to 20 microns. In contrast, electron micrographs showthat att-apulgite crystals attain a maximum length of only 4 to 5microns and a thickness of a mere 50 to A.

Thus, our product consists of particles which although apparentlynoncrystalline nevetheless have a definite geometrical form, Whereas rawclay (or extruded raw clay) milled to the same particle size, andcalcined under identical conditions, will appear under an opticalmicroscope as shapeless, granular masses. These facts indicate thatindividual elongated particles in our product have been derived from alarge number of attapulgite crystals, with the latter aligned in arelationship very different from the random brush heap arrangement ofcrystals in raw clay, extruded raw clay, or in simple clay slips whichhave been dried. This novel orientation of colloidal attapulgite needlesacquired by drying the quiescent, chemically deflocculated attapulgitedispersion is apparently set or preserved during the calcination of thedried product which takes place at a temperature at which theattapulgi-te crystal structure is destroyed and incipient sinteringoccurs.

In addition to the differences brought out above, there exist other andsignificant differences between our magnesium aluminosilicate productand known forms of attapulgite clay. One of the most apparentdifferences is that the bulk density of our material is appreciablylower than known forms of the parent attapulgite clay. For example, thebulk density of raw mildly dried clay is about 25 to 35 lbs/cu. ft.Activation increases the density to 30 lbs./ cu. ft. or more. Ourmaterial, although it has undergone a severe calcination which would beexpected to increase its bulk density considerably over that of rawclay, has a bulk density of only 12 to 20 lbs./ cu. ft., and usuallyabout 14 to 18 lbs./ cu. ft. All bulk density values reported hereinrefer to tamped bulk density values obtained by the settling methoddescribed in US. 2,477,3 86 to William S. W. McCarter.

Further, the surface area of our material is from 1 to 25 square metersper gram, which is significantly lower than the surface area of rawattapulgite clay or activated attapulgite clay, both of which havesurface areas in the neighborhood of 200 square meters per gram. Surfaceareas reported herein refer to so-called B.E.T. values determined afterdrying a sample at 350 F. by a nitrogen adsorption method described byS. Brunauer, P. H. Emmett, and -E. Teller in their article entitledAdsorption of Gases in Multi-molecular Layers, on page 309 of Journal ofAmerican Chemical Society, vol. 60, February 1938, using the molecularsize data of H. K. Livingston presented in his article entitledCross-sectional Areas of Molecules Adsorbed on Solid Surfaces, on page569, Journal of the American Chemical Society, vol. 66, April 1944.

The magnesium aluminosilicate products of our invention are equal to orsuperior to various commercial diatomaceous silica filter aids in theirclarity-flow relationship in the filtration of sugar solutions. As inthe case of dia tomaceous filter aids, the relatively high flow rateproducts of our invention generally yield a lower clarity filtrate thanthose products of our invention which have lower flow rates. Hence, acompromise must be made between flow rate and clarity in selecting thespecific processing steps, particularly the calcination step, whichdetermine these variables. In addition toacceptable flow rate andclarity, the products of the present invention form filter cakes whichare as firm and adhesive as cakes formed by diatomaceous silicaproducts.

It is believed that the unique shape of our novel fiberlike particlesaccounts for the efiectiveness of our material as a filter aid and thatsuch particles function in a manner similar to diatoms in building arigid porous filter cake during clarification. This belief iscorroborated by the results of numerous studies of the filtrationproperties of many types of clays (e.g., swelling bentonite, nonswellingbentonite, kaolin, attapulgite) processed by dry procedure and by theWet process of our invention.

Only the novel predominately fiberlike form of attapulgite produced bythe process of the present invention exhibited filtration propertiescomparable with those of diatomaceous earth filter aids in thefiltration of sugar solutions.

More specifically, the clay we use in our process is attapulgite clay inits natural hydrous form. The clay may be raw clay for reasons ofeconomy although clay which has been refined to eliminate coarse lumps,iron, quartz or other impurities may be employed. The clay may be driedsomewhat prior to use in our process. As is known to those familiar withclay minerals, drying of our clay to a V.M. less than about 18% impairsor eliminates the colloidal properties of the clay-i.e., the ability ofthe clay to be dispersed in water into its ultimate colloidallydimensioned particles. Therefore, the starting clay, if dried, must beone which has never been dried to a V.M. below about the 18% level. Insome instances, it may be advantageous to use raw clay which is mixedwith water to an extrudable consistency, e.g., a mixture having a V.M.of about 50% to 60%, extruded into pellets or the like and then mildlydried.

The clay is crushed, as to minus 4 mesh, and is slipped with watercontaining a defioccula-ting agent in a vessel provided with means foragitating the slip. The deflocculating agent may be added to anundispersed clay slip or the undispersed clay slip may be added to asolution of deflocculating agent. It is essential to agitate the clay inthe water to effect the required dispersion. Any high speed agitatorwill suffice. Typically, the clay solids content of the defiocculatedslip is from about 14% to about 18% of the weight of the slip,calculated on a volatile free clay basis. Slips as dilute as 10%volatile free clay solids may be used although the necessity for dryingthe larger quantity of water in subsequent processing will adverselyaffect the economy of such operation. We may use slips as concentratedas about 25% or somewhat more (based on the volatile free clay weight),although the ultimate product generally will not possess the same degreeof clarification efficiency as will a product prepared utilizing a lessconcentrated slip unless special reagents, e.g., NaOH, are used toenhance the clay dispersion at this high clay solids level. This maybe-explained by the importance of dispersing the attapulgite aggregatessubstantially completely into its ultimate coll-oidally dimensionedparticles. Obviously, the use of insufficient water in the slipping stepwill favor the presence of undispersed clay particles. It will be notedthat the quantity of water used in slipping our clay is substantiallygreater than the amount or water employed in the well-known priorpractice of extruding our clay with a plasticizing quantity of water toimprove its adsorptive properties or to enhance its gel-formingproperties. It Will be shown in the examples that follow that theextrusion of a mixture of our clay with water is an unsatisfactorysubstitute in our process for the step of forming a deflocculated clayslip.

As mentioned, a deflocculating agent, such as, for example, sodiumsilicate or tetrasodium pyrophosphate, must be employed to deflocculatethe colloidal attapulgite particles which possess interparticleattraction in the absence of the defloccula-ting agent. Thedeflocculating agent neutralizes or eliminates the interparticleattraction with a degree of efficiency which depends on theconcentration and capacity of the deflocculating agent. The action ofthe defioccu lator on the clay-Water slip is manifested by a markedthinning of the slip when the defiocculating agent is incorporatedtherein. In the absence of deflocculating agent, our clay dispersionswould be thickened systems, gel-like in character. The deflocculatingagent is used in an amount typically within the range of about 1.0% toabout 5.0%, based on volatile free weight of the clay. Particularly goodresults have been obtained using tetrasodium pyrophosphate in amounts ofabout 2.4%, based on the volatile free weight of the clay. In general,it may be said that the optimum quantity of deflocculating agent is thatwhich results in an aqueous slip of minimum viscosity. The clay contentof the slip will also influence the optimum quantity of defiocculator.Other materials used by the clay industry as deflocculating agents mayalso be used in case simple experimentation indicates that suflicientlyfluid slips of the desired solids level can be produced with theseagents. As examples of such defiocculating agents may be cited disodiumdihydrogen pyrophosp-hate, sodium tripolyphosphate, sodiumlign'osulionate, sodium salts of condensed naphthalene sulfonic acidsand corresponding potassium and lithium compounds when they aresufficiently soluble.

In some instances, the incorporation of a small amount of an inorganicsurface active agent in the slip will improve the dispersion of theclay. When used, the surface active agent is preferably added to apreviously deflocculated slip of clay, preferably with agitation whichdoes not effect substantia-laeration. The function of the agitation isto thoroughly disseminate the surface active agent in the slip withoutany aeration requirement since we have found that foaming the slipproduces no observable benefit in terms of the quality and nature of theultimate product. The surface active agent must be soluble ordizspersible in the slip and must not coagulate the clay dispersion. Theoptional organic surface active agent is not a satisfactory substitutefor our essential deflocculasing agent and it merely supplements theaction of the deflocculating agent.

The presence of materials which will i'locculate or coagulate thedeficcculated clay dispersion is to be avoided.

The aqueous clay slip, in the form of a dispersion of iluid consistency,is then dried to a giindable consistency by evaporation of water fromthe slip. As mentioned, the fluid clay dispersion is maintainedquiescent or immobile during drying which may be carried out underatmospheric pressure or under vacuum. While it is being dried, thetemperature of the slip is maintained below the boiling point at thepressure employed so that little or no cbullience of the slip occurs.For practical reasons, we prefer to dry our slip while it is in the formof a thin film, e.g., a layer about ,6 to 1" deep. Tray driers andconventional drum driers are useful in carrying out the drying step.Experience has shown that the material is preferably dried to a V.M. notless than 5%, and usually to a V.M. within the range of 12% and 30%,Material dried to a V.M. less than about 5% produces ex cessiveundesirable fines (cg, particles finer than about 2 microns) during thesubsequent milling step. 011 the other hand, material having a V.M.considerably greater than 30% may be diliicult to grind to the desireddegree of fineness. However, by appropriate choice of grindingequipment, drying to a V.M. higher than 30% may be satisfactory. Theparticle size desired in the product will determine the optimum V.M. ofthe dried material. Excellent filter aid products have been preparedwhen the slip was dried to a V.M. from 12% to 17%.

Although filtration might suggest itself as an alternative method fordewatering the slip, it has been found that the desired ultimatemicroscopic fibrous product will not be produced when the slip isdewatered by filtration. This observation corroborates our belief thatevaporation of water from the defloccula ted clay slip results in a moreordered, probably layerlike reorientation of aligned individualattapulgite particles, much like asbestos aggregates. Filtration wouldbe expected to inhibit such an orderly reorientation as a result ofcompression on the particles during the dewatering of the slip.

The dried material is then ground to about 100% minus 200 mesh in anysuitable mill, such as a Mikro- Pulverizer (a high speed hammer mill),ball mill, roller mill or cage mill. The degree of fine grinding will bedetermined by the properties desired in the filter aid product. It isknown that the clarity-fiow rate correlation of filter aids vary withthe particle size distribution of the filter aid and this property canbe controlled at this point of the process. Thus, the material may beground somewhat coarser than 200 mesh or somewhat finer, if desired.

The ground intermediate product has many properties normallycharacteristic of raw attapul-gite. For example, the clay is stillcrystalline and retains colloidal and ad- &

sorptive properties typical of raw clay. This product is transformed bycalcination at a temperature sufiicient to eliminate substantiallycompletely the water of hydration and free moisture from the claylattice but at a temperature below the fusion point of the mass.Incipient sintering appears to occur. Removal of water from the claylattice eliminates the colloidal, gel-forming properties of the clay anddestroys the clay lattice, forming an amorphous anhydrous material whichcannot accurately by called attapulgite. The calcination temperature isusually between about 1300 F. and 2200 'F. or somewhat higher. Thecalcination time is from 15 minutes to several hours, depending on theequipment and temperature, and is sufiicient to reduce the product V.M.to a value less than 1%. The preferred temperature and time will dependon the furnace in which calcination is carried out and will generallyvary between about 1400 F. and about 1800 F. the optimum calcinationtempera ture will vary considerably with the intended use of the filteraid product and the clarity-filter rate relationship desired in thematerial. By way of illustration, it may be said that when optimumclarity is sought with some sacrifice in flow rate in the filtration ofsugar or other aqueous solutions, a calcination temperature of the orderof 1500 F., for example, will @be employed rather than 1750 F. On theother hand, calcination at the higher temperature level may result in aproduct having a substantially higher filter rate for aqueous solutionsalthough somewhat lower clarification capacity than the product calcinedat the lower temperature and may 'be the preferred temperature when theproduct is intended for such use. In the filtration of organic liquidsthe effect of calcination temperature on filtration rate may be lesspronounced than when aqueous liquids are filtered. Thus, in thefiltration of organic liquids, the higher clarities obtainable withproducts calcined at temperatures closer to the lower end of thetemperature range set forth above may make the use of such lowertemperatures preferable. When organic surfactants have been used,calcination is carried out in the presence of sufiicient air or in otheroxidizing atmosphere to burn off any organic matter used in thepreparation of the product. Calcination also incorporates thenonvolatiles of the defluoccu-lating agent in the product and reducesthe surface area of the clay, thus in effect thermally deactivating theattapulgite.

The calcined product is composed of friable masses of loosely aggregatedfine particles. These masses are disaggregated by mild pulverization.Many apparatuses are suitable for the purpose, among which may bementioned hammer mills operated with slow moving hammers and rollermills. 'I hese mills may be equipped with classifiers if strict controlof product particle size is desired. Simple dry screening devices willalso sufiice to break up the aggregates into the individual fine filteraid particles.

If desired, materials such as calcite flour or magnesite, for example,may be incorporated with the calcined prodnot for pH adjustment when theproduct is intended for use in clarifying sugar solutions.

The following examples are given for illustrative purposes only and arenot to be construed as limiting our invention to the specific detailsset forth herein.

In the examples the flow rate testing was performed in a bomb filtertest unit. The unit consisted of a vertical metal tube flanged at thebottom so that it could be bolted to a horizontal circular filter platewhich supported a filter cloth and had a vertical opening through thecenter to permit fluid flow. A discharge valve with a threaded end wasscrewed to the underside of the filter plate. The filter area was 1.0square inch. The tube assembly was enclosed in a circulating heated oilbath for temperature control. Measurements were made on the unfilteredand filtered solutions using a Klett Summerson Photoelectric uColorimeter to determine degree of clarity. A red glass filter was used.

A mixture containing 10% raw sugar and 90% refined sugar was dissolvedin sufficient water to produce a 46-47 Brix solution. The filter aid wasthen added at a 1.33% weight dosage to the solution and the contentsheated to 100 F. This slurry was then poured into the bomb filter. Thebomb was capped and immediately pressurized with nitrogen to 50 psig.before opening the flow discharge valve. The discharge valve was openedone minute after changing the solution. The filtrate volumes andcorresponding time intervals were measured and recorded. The flow ratewas calculated from time required for 5 cc. of solution to flow throughthe filter aid. Clarity and turbidity measurements were made on the 100to 500 cc. composite filtered solution.

The absolute flow rate and clarity values were converted to index valuescompared with the corresponding values determined by tests made on astandard filter aid product and were determined by assigning theabsolute flow rate and clarity values of the standard silica filter aidproduct the index values of 100 and 100, respectively. The standardfilter aid was Hyflo Super-Ce'l, a flux-calcined diatomaceous silicaproduct consisting predominantly of 8 to 38 micron particles.

EXAMPLE I Experiments were performed to deter-mine the filtrationcharacteristics of attapulgite products dry processed in accordance withthe prior art by drying raw clay to various volatile matter contents(hereafter set forth), grinding to minus 200 mesh, calcining at 750 F.to volatile matter contents within the range of 1% to 6 and screeningthe calcined product to recover a minus 200 mesh product. Runs were alsomade to determine whether merely calcining the dried, milled raw clay atmore elevated temperatures than taught by the prior art (to eliminatesubstantially volatile matter) would result in a filter aid productcomparable with the diatomaceous earth standard. Also studied was acommercial activated attapul-gite product. The results are reported inTable I.

Table I FILTRATION PROPERTIES OF ATTAPULGITE PROD- UCTS-46-47 BRIX SUGARSOLUTIONS Flow rate Clarity index index Attaelay LVM, Minus 200 Mesh 4124 Raw Clay, Dried to 18.5% V.M., Ground 200 Mesh, Calcined 750 F./30Min 5 124 Raw Clay, Dried to 277 V.M. Ground to -200 Mesh, Caleined750F. 30 Min 5 112 Raw Clay, Dried to 14.4% V.M. Ground to 20() Mesh,Calcined 750 F./30 Min 19 92 Raw Clay, Dried to 18.5% V.M., Ground to200 Mesh, Calcined 1,750 F./30 min 23 80 Raw Clay, Dried to 27% V.M.,Ground to 200 Mesh, Calcined 1,750 F./30 Min 124 Raw Clay, Dried to14.4% V.M., Ground to Mesh, Caleined 1,750 I i/ Min 13 120 1 Acommercial activated attapulgite clay product; V.M. (as produced) 68%,1?.M. (as produced) 0.2%.

The results reported in Table I show that all of the dry processedattapulgite clays, i.e., the commercial product and those prepared inaccordance with prior art procedure or modification thereof, hadextremely low flow rate indexes as compared with the silica standard;

EXAMPLE II ture in a tetrasodium pyrophosphate solution to 18.8% solidsin a Denver Conditioner (a paddle-agitated vessel used in theconditioning of ores for flotation). The tetrasodium pyrophosphatecontent of the slip was 2.4%, based on the volatile free weight of theclay. The resultant fluid slip was placed in trays in a layer 1" deepand the trays were placed in an oven maintained at 300 F. until the V.M.of the slip was 14.6%. The drying conditions were such that the slip wasquiescent and no boiling occurred. The dried material was crushed in aroller mill and ground in a high speed hammer mill using a 0.020"screen. The minus 200 mesh material was calcined at 1750" F. for 30minutes and the calcined material was screened through a 200' meshscreen using a RoTap classifier.

The flow rate index of the minus 200 mesh product was 106 and theclarity index was 98. The flow rate index of the product wassubstantially higher than that of any of the attapulgite clay productsof Example I.

The results, compared with those of the previous example, show thesuperiority of a filter aid product of this invention over attapulgiteproducts which have been similarly sized and calcined at varioustemperatures without the preliminary formation of a thin, fluiddeflocculated aqueous dispersion of the clay.

EXAMPLE III This example illustrates the generally inverseclarification-flow rate relationship of the products of our inventionand shows that various attapulgite products may be produced withfiltration properties comparable with or superior to those of variouscommercial grades of diatomaceous silica filter aids.

In the preparation of filter aid products of our invention, rawGeorgia-Florida fullers earth from a deposit near Attapulgus, Georgia,was used. The clay was slipped at room temperature for about 5 minutesin a large Waring Blendor at an 18% by weight clay solids level (basedon the volatile free weight of the clay) in a dilute aqueous solution oftetrasodium pyrophosphate. The tetrasodium pyrophosphate was used in theamount of 2.4%, based on the volatile free weight of the clay in theslip. The resultant fluid slip was then conditioned at room temperaturefor 5 minutes in the Waring Blendor with the sodium soap of tall oilfatty acids, in the amount of 1.5% of the volatile free weight of theclay. The conditioned slip had a thin creamlike consistency with only asmall amount of foam on the surface. Portions of the slip were placed intrays in a layer 1" deep. The slips were tray dried in an oven held atless than 250 F. to a volatile matter content of 15% to 17%. Dryingconditions were such that the slip was quiescent and no boilingoccurred. The dried material was crushed in a roller mill and ground ina high speed hammer mill using a 0.027" screen. The pulverizedintermediate product was calcined (at temperatures and for timesreported below) in a static bed muffle furnace. The calcined productsconsisted of friable lumps which were pulversized by screening through a200 mesh screen (using a RoTap screener).

The filtration properties of filter aid products prepared as describedabove were compared with those of the following commercial diatomaceoussilica filter aids, which are listed in order of decreasing clarityindex (and increasingflow rate index): Celite 505, a high clarity-lowflow rate product; Hyflo Super-Cell; Celite 502, believed to be aflux-calcined diatomaceous silica product; and Dicalite Speed Flow.

The processing variables and filtration characteristics of theattapulgite-based filter aids and commercial diatomaceous silica filter"aids on sugar solutions (as determined by the test procedures describedabove) are re ported in Table II.

Table 11 Flow Clarity Cake Attapulgite products Calcination rate indexthicktempJtimc index ness,

inches Sample N011 1,750 F./30 Min 169 93 V6 Sample No 2 1,650 F./30lVIin 88 104 M Sample No 3" 1,550 F./30 Min 37 117 3 15 Celite 505 130Dicalitc Speed Flo 38 108 %6 Hyflo Super-Ce1 100 100 %[1 Celite 503 14591 1 Standard.

The results show that the flow rate-clarity relationship of filter aidproducts made from attapulgite by the process of the present inventionmay be controlled by calcination temperature. The results also show thatgrades of attapulgite-derived products can be produced with filtrationproperties comparable and in many instances superior to those ofcommercial diatomaceous silica products, even the high flow rate gradesof diatomaceous silica. All other influencing variables being keptconstant, calcination at 1550 F. (sample No. 3) produced a highclarity-relatively low flow rate product. Calcination at 1750 F.resulted in a product (sample No. 1) which had a substantially higherilow rate although somewhat lower clarity index than sample No. 3 andwhich had a higher flow rate index at substantially the same clarityindex as the standard (Hyflo Super-Gel).

EXAMPLE IV This example illustrates the preparation, in accordance withthis invention, of a filter aid from attapulgite clay using a sodiumsilicate as the deiiocculatin agent.

Raw Georgia-Florida fullers earth from a deposit near Attapulgus,Georgia, was slipped for about 5 minutes in a large Waring Blender at asolids level in an aqueous solution of sodium silicate, using 8% sodiumsilicate solution, based on the volatile free weight of the clay. Thesodium silicate was a 426 B. solution analyzing 9.10% Na O and 29.6% SiOThe slip was conditioned for 5 minutes in the Waring Blendor with 1.5%,based on the volatile free weight of the clay, of sodium soap of talloil fatty acids. The slip was dried in trays (without agitation orboiling) in an oven held at less than 250 F. to a volatile mattercontent of about 16%. The dried material was crushed in a roller milland ground in a Mikro-Pulverizer using a 0.027" screen, calcined in airat 1750 F. for 30 minutes in a mufile furnace and screened through a 200mesh screen. The product was found to have a filter rate index andclarity index of 120 and 103, respectively. The product was thussuperior to the standard, particularly in its filter rate.

EXAMPLE V Various surface active agents including materials of anionic,nonionic and cationic character, were employed in the preparation offilter aid products from attapulgite clay in accordance with our processand the filtration properties of these products were determined. Thefollowing surface active agents were employed: Monamid 15-70W andMonamid -150-ADD, which are nonionic fatty acid alkanolamides and areproduced, respectively, by reaction of mixed unsaturated fatty acidswith diet]:- anolamine and refined coconut oil fatty acid withdiethanolarnine; red oil, which is an anionic material; Kessco X468, acationic substituted imidazoline produced from oleic acid andaminoethylethanolamine; Nalcamine G- 39M, a cationic material which is1(2-aminoethyl)-2- (mixed heptadeccnyl andheptadccadienyl)-2-imidazoline; Arquad 16, which is cationic andconsists mainly of trirnethyl-n-hexadecylammonium chloride.

In the preparation of the filter aid products, ra-w clay was pugged withwater to a V.M. of 65%. The clay was from the same deposit as the clayused in the previous 12 examples. The pugged material was slipped for anhour in a paddle agitated vessel to 18.1% solids (based on the volatilefree clay weight) in water in which was dissolved 2.4% tetrasodiumpyrophosphate (based on the volatile free weight of the clay). The slipwas conditioned in a Fagergren agitator air off) for 5 minutes with 1.5%of surface active agent (based on the volatile free weight of the clay).Each conditioned slip was placed in a 1" layer in trays which wereplaced in an oven held at less than 250 F. Each slip was dried withoutagitation to a V.M. of 16% to 17%. The dried materials were crushed in aroll crusher, ground in a high speed hammer mill to minus 200 mesh andcalcined at 1750 F. for 30 minutes. The calcined products were screenedthrough a 200 mesh screen on a RoTap machine and the minus 200 meshmaterial inspected in a microscope at (810x) and also evaluated forclarification index and flow rate index.

All of the products appeared in the microscope as heing composed of apredominant amount of discrete elongated irregular fibers (or branchedarrangement of such particles).

The filtration properties of the various products are tabulated in TableIII.

The results reported in Table III show that products of this inventionhad a clarification index comparable with that of the commercialdiatomaceous silica filter aid standard at a correspondingly high flowrate value.

EXAMPLE VI This example illustrates the necessity of obtaining a gooddispersion of the clay in the slipping step in order to obtain a productwhich has flow rate and clarification properties comparable withcommercial diatomaceous filter aids.

In the investigation 18% solids slips'of attapulgite clay were made upin a Waring Blendor using 1.5% and 2.4% tetrasodium pyrophosphate (basedon the volatile free weight of the clay). Slipping time was 5 minutes.Each slip was conditioned for 5 minutes in the Waring Blender with 1.5%(based on the volatile free weight of the clay) of tall oil soap. Theslips were dried at "F. to 16% V.M., crushed, ground to minus 200 meshin a high speed hammer mill, calcined at 1750 F. for 30 minutes andpulverized by screening through a minus 200 mesh screen. The propertiesof the minus 200 mesh product are reported in Table IV.

C-cationic. Aanionic.

Table IV Percent tetrasodium pyrophosphate Flowrate Clarification indexindex particles were observed only in the product obtained with 2.4% ofdefiocculating agent. Although 1.5% deflc culator appeared to beinsufiicient to disperse the clay with the equipment, procedure andparticular sample of clay involved, this level of deflocculator mayproduce very satisfactory dispersions when using less concentrated clayslips or by employing attapulgite clay from other deposits or by puttingmore work into the slip.

EXAMPLE VII This example illustrates that extrusion of water-plasticizedraw attapulgite clay, as taught in the prior art, in conjunction withsizing and calcining, is not a satisfactory substitute for the step ofproducing a defiocculated aqueous dispersion of attapulgite clay in theproduction of a filter aid. v

A sample of raw Georgia-Florida fullers earth (V.M. 50%) from a minenear Attapulgus, Georgia, was crushed to minus 4 mesh and mixed in a pugmill with an equal weight proportion of water. The mixture was puggedfor about 10 minutes and the pugged mixture was extruded in an angerextruder through a die having a %-lI1Cl1 land. The extrudate was driedin an oven at about 300 F. to a V.M. of 21% and the dried extrudate waspulverized by a single pass through a Mikro-Pulverizer (6 hammers) usinga 0.020-inch screen. The pulverized material was calcined in a mufliefurnace at a chamber temperature of 1750 F. for 30 minutes. The calcinedagglomerated material was placed on a RoTap shaker and screened througha 200 mesh screen. The average particle size of the product was 19microns.

The flow rate index and clarification index of this product were 44 and68, respectively. These values, as compared with the results of Example11, indicate that merely mixing the raw clay with water and extrudingthe wet mixture is not the equivalent of producing a dellocculated claydispersion in the production of a filter aid from attapulgite clay.

EXAMPLE VIII This example illustrates that attapulgite is unique amongcolloidal clay minerals in that when it is processed in accordance withan example of the wet method of our invention, it produces a productcontaining a predominating amount of unique microscopic irregularelongated particles, whereas other clays do not. This exampleillustrates further the superiority of our wet processed attapulgiteclay as a filter aid over other clays, dry or wet processed.

The clays investigated were attapulgite clay; Wyoming bentonite (asodium montmorillonite clay frequently referred to as swellingbentonite); and southern bentonite or sub-bentonite as it is sometimescalled, which is a calcium montmorillonite and, unlike sodiummontmorillonite, is a nonswelling clay. Also investigated was a Georgiakaolin clay.

The general procedure followed in wet processing the various claysinvolved forming an 18%solids clay slip in water in which was dissolved2.4% tetrasodium pyrophosphate (based on the volatile free weight of theclay). A Waring Blendor was employed and slipping time was minutes. Inthe case of Wyoming bentonite this step had to be modified to form a 10%sol-ids slip since this clay could not be dispersed at the 18% solidslevel. 1.5% sodium soap of tall oil fatty acid (based on the volatilefree Weight of the clay) was added to each slip and uniformly mixedtherein by agitating the soap-conditioned slip for 5 minutes in theWaring Blender. The slip was then dried without agitation (in a 1 deeplayer) in a tray held in an oven maintained at less than 250 F. to aV.M. of to 20%. The dried slip was crushed in a roll crusher and groundto minus 200 mesh in a high speed hammer mill, calcined for /2 hour at1750 F., and the calcined product screened through a 200 mesh screen.

(a) The minus 200 mesh product produced by wet processing each of theabove-mentioned processed clays was observed under an optical microscope(810x Only those products which were prepared from attapulgite containeda predominating amount of elongated particles. The other clays resultedin products which appeared as shapeless granular masses with no evidenceof elongation of particles.

(b) Samples of some of the aforementioned clays were dry processed bycalcining the raw clay at 1750 F. for 30 minutes (without previousslipping) and grinding the calcined material to minus 200 mesh. Theproducts were studied under an optical microscope (810x) and none wasfound to show any evidence of elongated particles.

(0) The filtration characteristics of each of the Wet and dry processedclays of Example VIII (a) and (b) were measured. Only the Wet processedattapulgite which appeared fibrous under the microscope was found tohave clarity-flow rate index comparable with commercial grades ofdiatomaceous earth filter aids. The clarity-flow rate indexrelationships of the various products are reported in Table V.

Table V The results show that of the processed clays only the wetprocessed attapulgite provided a thick filter cake and had bothhighclarity index and high flow rate index. Wet processing produced noobservable benefit in the case of the bentonites. Kaolin was completelyunacceptable as a filter aid.

lt will be understood that the foregoing detailed examples areillustrative only, for variations and changes may be made in theconditions of the process without departing from the substance of theinvention as herein disclosed and defined in the appended claims.

We claim:

1. A method of treating attapulgite clay to render it useful as a filteraid which comprises providing a thin aqueous dispersion of colloidalattapulgite clay utilizing a defiocculating agent for said clay, dryingsaid dispersion by evaporating water therefrom so as to form a materialof grindable consistency while maintaining said dispersion quiescent,grinding the dried material and calcining the ground material at atemperature and for a time sulficient to substantially eliminatevolatile matter therefrom without fusing the material.

2. A method of treating attapulgite clay to render it useful as a filteraid which comprises agitating a small amount of attapulgite clay whichhas never been dried to a V.M. less than about 18% in water containing adeflocculating agent for said clay so as to form a deflocculated aqueousdispersion of said clay, drying said dispersion by evaporating watertherefrom so as to form a material of grindable consistency whilemaintaining said dispersion quiescent, grinding the dried material andcalcining the ground material at a temperature and for a 35 timesufiicient to eliminate substantially volatile matter therefrom Withoutfusing the material.

3. A method of treating attapulgite clay to render it useful as a filteraid which comprises agitating a small amount of colloidal attapulgiteclay in a dilute aqueous solution of tetrasodium pyrophosphate so as toform a thin deflocculated aqueous dispersion of said clay, drying saiddispersion by evaporating water therefrom to form a material ofgrindable consistency while controlling the temperature and restrictingagitation so as to maintain said dispersion quiescent during drying,grinding the dried material, calcining the ground material at atemperature within the range of from about l500 F. to about 2200 F. fora time sufiicient to eliminate substantially volatile matter andpulverizing the calcined material.

4. A method or" treating attapulgite clay to render it useful as afilter aid which comprises providing an aqueous slip of colloidalattapulgite clay utilizing tetrasodium pyrophosphate as a deflocculantfor said clay, drying said slip by evaporating water therefrom at atemperature below which said slip is ebullient and without agitatingsaid slip to form a material of grindable consistency, grinding thedried material, calcining the ground material at a temperature withinthe range of from about 1400 F. to about 1800 F. for a time sufiicientto substantially eliminate volatile matter therefrom and pulverizing thecalcined material.

5. A method of treating attapulgite clay to render it useful as a filteraid which comprises providing an aqueous slip of colloidal attapulgiteclay utilizing sodium silicate as a deflocculant for said clay, dryingsaid slip by evaporating water therefrom at a temperature below whichsaid slip is ebullient and without agitating said slip to form amaterial of grindable consistency, grinding the dried material,calcining the ground material at a temperature within the range of fromabout 1400 F. to about 1800 F. for a time sufiicient to substantiallyeliminate volatile matter therefrom and pulverizing the calcinedmaterial.

6. A method of treating attapulgite clay to render it useful as a filteraid which comprises agitating a small quantity of colloidal attapulgiteclay in an aqueous solution of a deflocculating agent for said clay soas to form a thin deflocculated clay dispersion, drying said dispersionin the form of a film about 1/64 to 1 thick by evaporaing watertherefrom while maintaing said film quiescent to form a material ofgrindable consistency, grinding the dried material, calcining the groundmaterial at a temperature Within the range of from about 1400 F. toabout 1800 F. for a time sufiicient to substantially eliminatecompletely volatile matter therefrom and pulverizing the calcinedmaterial.

7. A method of treating attapulgite clay to render it useful as'a filteraid which comprises dispersing a small amount of colloidal attapulgiteclay in Water having dissolved therein a deflocculating agent for saidclay to form a thin fluid deflocculated aqueous dispersion of said clay,drying said dispersion to a V.M. of about 12% to 30% in the form of athin layer thereof by evaporating water therefrom while maintaining saiddispersion quiescent, grinding the dried material, calcining the groundmaterial at a temperature and for a time sufl-icient to reduce thevolatile matter content thereof below 1% without fusing the material,and pulverizing the calcined material.

8. A filter aid comprising essentially an anhydrous magnesiumaluminosilicate in the form of amorphous elongated particles ofmiscroscopic dimensions and having a surface area of about 1 to 25square meters per gram, a tamped bulk density of 12 to 20 lbs/cu. ft.and essentially the same chemical analysis as volatile-free attapulgiteclay.

9. Thermally treated attapulgite clay, useful as a filter aid,characterized by having a surface area of about 1 to 25 square metersper gram, a tamped bulk density of 12 to 20 lbs/cu. ft. and essentiallythe same chemical analysis as volatile-free attapulgite clay, themajority of the particles of said thermally treated attapulgite claybeing in the form of elongated particles of microscopic dimen- 810118.

10. Thermally treated attapulgite clay, useful as a filter aid,characterized by having a surface area of from 1 to 25 square meters pergram, a tamped bulk density of 12 to 20 pounds per cubic foot, a V.M.less than 1% and essentially the same chemical analysis as volatile-freeattapulgite clay, the majority of the particles of said thermallytreated attapulgite clay being in the form of elongated particles havinga Width within the range of 2 to 5 microns and a length within the rangeof 5 to microns.

11. The product of claim 10 in which the majority of the particles arewithin the range of 2 to 3 microns Wide and within the range of 10 to 20microns long.

References Cited in the file of this patent UNITED STATES PATENTSCatlett Jan. 3, 1899 Miketta Apr. 29, 1930

1. A METHOD OF TREATING ATTAPULGITE CLAY TO RENDER IT USEFUL AS A FILTERAID WHICH COMPRISES PROVIDING A THIN AQUEOUS DISPERSION OF COLLODIALATTAPULGITE CLAY UTILIZING A DEFLOCCULATING AGENT FOR SAID CLAY, DRYINGSAID DISPERSION BY EVAPORATING WATER THEREFROM SO AS TO FORM A MATERIALOF GRINDABLE CONSISTENCY WHILE MAINTAINING SAID DISPERSION QUIESCENT,GRINDING THE DRIED MATERIAL AND CALCINING THE GROUND MATERIAL AT ATEMPERATURE AND FOR A TIME SUFFICIENT TO SUBSTANTIALLY ELIMINATEVOLATILE MATTER THEREFROM WITHOUT FUSING THE MATERIAL.
 8. A FILTER AIDCOMPRISING ESSENTIALLY AN ANHYDROUS MAGNESIUM ALUMINOSILICATE IN THEFORM OF AMORPHOUS ELONGATED PARTICLES OF MISCROSCOPIC DIMENSIONS ANDHAVING A SURFACE AREA OF ABOUT 1 TO 25 SQUARE METERS PER GRAM, A TAMPEDBULK DENSITY OF 12 TO 20 LBS./CU. FT. AND ESSENTIALLY THE SAME CHEMICALANALYSIS AS VOLATILE-FREE ATTAPULGITE CLAY.